Abstract

Hydrogen production could be used to consume excessive renewable energy. Many energy management systems (EMSs) were proposed to link hydrogen production with renewable farms. The majority of the studies, however, are not based on the real-life systems and do not fully utilize the potential of demand response from P2X components. In this paper, we propose an EMS architecture based on the GreenLab Skive industrial cluster that can operate the system with default, economic (minimize operational costs) and sustainable (produce green hydrogen) schedules. EMS utilizes the flexibility from electrolyzer, hydrogen tank, battery and hydrogen consuming plants (HCPs) to provide an optimal dispatch in the economic and sustainable schedule; operating the system in either of them results in operational costs reductions in comparison with default schedule. The hydrogen produced with the sustainable schedule is green and such operation could serve as a backbone of the future sustainable energy system.

Abstract

Carnot Batteries are a promising approach to store electrical energy in a thermal way. Besides the loading and unloading thermodynamic processes, the heat storage is a field of mayor interest in research. This paper presents an innovative modular storage setup that is easily scalable and contains an immiscible liquid phase to separate the hot and cold side of a sensible water storage. The separation of hot and cold side thus reduces the heat losses and improves the efficiency of the whole storage concept. A pilot plant to study the idea experimentally is in construction.

Abstract

In this study, a computational fluid dynamics (CFD) model was developed to study the flow and heat transfer characteristics of a 320 MW oxy-fired boiler with dry and wet flue gas recirculation (FGR). The results show that there exist significant differences in the composition and physical properties of flue gas between the air- and oxy-combustion modes and these differences may lead to remarkable differences in the flow, temperature and heat transfer distributions of boiler. Specifically, since the specific heat of CO2 and H2O are higher than that of N2, the flue gas heat capacity of the oxy-combustion case with wet FGR is significantly higher than the air-combustion case leading to lower furnace temperature and heat absorption of furnace wall. Moreover, since the density of CO2 is higher than N2, the overall flow velocity in oxy-fired boiler is lower than that of air-fired boiler, which subsequently affects the boiler flow and temperature distributions in the furnace. The differences in the flow and heat transfer distributions between oxy-fired and air-fired boilers should be taken into consideration when designing new oxy-fuel combustion systems or retrofitting existing air combustion systems to minimize costly modifications to the boiler’s heating surfaces.

Abstract

To investigate the release and transformation of fuel potassium during biomass gasification, paulownia wood is used in a fixed-bed reactor system during 500−900 °C. Chemical fractionation analysis are performed to study the existing form of fuel potassium. The influences of particle size and gasification temperature are discussed. The results show that release ratio of potassium increases with the gasification temperature. When the temperature is higher than 700 °C, the content of water-soluble and NH4Ac-soluble K decreases, and part of other occurrence modes of K turn into the insoluble K gradually. The release ratio of potassium with three different particle sizes reaches 26.65%, 32.53% and 40.56% respectively at 900 °C. Increase of particle size inhibits the potassium release and induces the formation of NH4Ac-soluble K. For centimeter-sized samples, potassium content at central is higher than that of surface at 700 °C, which is related to the formation of NH4Ac-soluble potassium. The content of potassium at different positions decreases significantly above 700 °C.

Abstract

Water washing pretreatment could alleviate the problems of ash deposition and slagging during the combustion of biomass. A large amount of washing leachate will be produced during the washing process. In this study, two kinds of biomass (corn stalk, rice husk) are selected as the research object. The combustion characteristics of the crystalline product of the water-washed leachate are studied by a thermal synchronization analyzer. The influence of biomass species and washing temperature on the combustion characteristics of leachate crystallization products was analyzed. The results show that the maximum combustion rate of the leachate crystals of corn stalk increases with the decrease of heating rate. The ignition temperature of the crystalline product of the corn stalk washing leachate increases with the increase of washing temperature. The ignition temperature of rice husk leachate crystals with the washing temperature at 60°C is higher than 30 and 90°C. Compared with the corn stalk leachate crystals, the rice husk leachate crystals have a lower ignition temperature. It is important to investigate the combustion characteristics of biomass leachate crystals which could provide the assistance in the treatment of leachate after washing.

Abstract

Water washing pretreatment is an effective method to remove alkali metals and chlorine elements in biomass, which could improve the performance of ash deposition and slagging of biomass fuels. In this study, two typical biomass fuels were pretreated with water washing. The effect of water washing on the ash fusion characteristics was carried out. According to the ash fusion characteristics test experiments, four characteristic temperatures and ash fusion dynamic curves of biomass ash samples were obtained, and the corresponding relationship between characteristic temperature and dynamic curve was studied. The results show that the fusion process of biomass ash contains four stage including shrinkage, expansion, melting and flow. Water washing can increase the deformation temperature of biomass ash by about 300 °C and the flow temperature by 150 °C, which can significantly reduce the biomass ash slagging.

Abstract

Oxygen reduction reaction (ORR) is an important electrochemical reaction in fuel cells (FCs). Until now, Pt and its alloys are still the best materials for ORR. However, the problem lies on how to prepare a high- performance catalyst with the lowest usage of Pt. Metal organic frameworks (MOFs) that represented by Zeolitic imidazolate framework(ZIFs) have been used as precursors for efficient transition metal-nitrogen- carbon (M-N-C, M=Fe, Co, Mn, et. al) catalysts ORR catalysts. However, these catalysts are generally reported to suffer from poor activity. In this paper, a low Pt catalyst Pt-NC-900 was synthesized by dispersing Pt on cubic ZIF-8 with highly usage for Pt. Cetyltrimethylammonium bromide (CTAB) was used to control synthesize cubic ZIF-8 in the aqueous phase. This synthesis method was a green process because no methanol was required. As synthesized ZIF-8 displayed a large specific surface area of 1870 m2/g. Subsequently, Pt was loaded on the carbon support with high pyridinic N content that obtained through heat treatment atmosphere and temperature optimization. The sample was treated under N2 atmosphere at 900℃ to obtain Pt-NC-900. It showed an optimal electrochemical performance with a half-wave potential (E1/2) of 0.84 V, which is 10 mV higher than Pt/C20% catalyst. and the Pt-NC-900 also showed a higher mass activity (0.207 A/mgPt) than Pt/C20%. The excellent ORR performance could be attributed to the Pt active centers, large specific surface area, rich pore structure, and high pyridinic-N content.

Abstract

Phase change material (PCM) gradually becomes a promising approach to keep the temperature within a comfortable range in the application of thermal management of electronic devices nowadays. In this work, TiO2 nanoparticles, copper foam and n-octadecane were composited by vacuum method to prepare nanoPCM(nanoparticle-phase change material) and the melting process of nano-PCM under the effects of different nanoparticle concentrations and ultrasonic powers were experimentally investigated. The results showed that the ultrasonic and nanoparticles in the melting process have positive effects on shortening the melting time of nano-PCM. As the ultrasonic power reached 100 W and the nanoparticle concentration reached 5 wt.%, the melting time of nano-PCM was reduced by 46.96%. In addition, the extra heat was found in the melting process brought by the heating effect of ultrasound. Finally, the heat source temperature increased with the increasing of ultrasonic power. Therefore, the relationship between the melting rate of nano-PCM and the heat source temperature needs to be balanced reasonably.

Abstract

In order to reduce battery aging and energy loss, an optimized charging method considering battery aging and energy loss is proposed in this work. Firstly, based on the second-order RC equivalent circuit model, the parameters of the battery model are identified by pulse current tests. Secondly, according to Joule’s law, the model of battery energy loss is established. Combining the established model with the aging empirical model, the dual objective of charging optimization is constructed. The non-terminated sorted genetic II algorithm is used to optimize goals. The utopian point method is applied to select the best target and determine the optimal charging current sequence. Finally, the effectiveness of the proposed method is verified by comparative experiments. The experimental results show that the overall effect of 8-stage current charging is better than that of 4-stage charging, which has better benefits for improving battery performance.

Abstract

In the real application of on board hydrogen production for fuel cell powered vehicle, the catalyst concerning steam reforming of methanol (MSR) for hydrogen production suffered frequent oxidation considering the intermittent driving of vehicle. In this study, the environment effect on the PdZn catalyst concerning MSR was investigated and the reason was discussed. It was found that a high molar ratio of Zn to Pd for intermetallic PdZn catalysts is favorable for the formation of PdZn intermetallic compound when the catalyst was oxidized and then reduced. The high molar ratio of Zn to Pd can guarantee the negligible influence of frequent oxidation on the catalytic activity and selectivity.